This invention relates to apparatus for bracing a tilt-up wall panel. More particularly, the invention relates to bracing apparatus which includes panel brace assemblies and knee brace assemblies.
Tilt-up construction is a job-site form of precast concrete construction. It involves prefabricating concrete wall panels or slabs flat on either the building floor slab or a temporary casting slab, then lifting or "tilting" them up with a mobile crane and carrying them to their final locations, where they are installed as vertical wall panels and become integral parts of the completed structure. In the erection of a tilt-up wall panel, the panel is connected temporarily to lifting to hoisting equipment, utilizing accessory lifting apparatus connected to the panel, and the panel is raised from the horizontal position in which it is cast to a vertical position. The raised wall panel is braced to support it while construction of the wall and other structure is completed. U.S. Pat. Nos. 2,684,824 and 3,798,856 illustrate two types of bracing apparatus employed in the past.
The lifting apparatus connected to a wall panel includes an anchor insert which is embedded permanently in the panel, and a pickup unit which is releasably connected to the insert and thereby to the panel, by fastening means engaging the insert. The pickup unit also is releasably connected to the lifting equipment. In practice, a plurality of inserts is embedded in a concrete panel by pouring wet concrete therearound and setting the concrete, and a pickup unit is connected to each embedded insert and also to the lifting equipment.
At the same time that the inserts of the lifting apparatus are embedded in the concrete forming the panel, similar inserts are embedded for connection to panel brace assemblies or braces. The brace assemblies generally are constructed of lumber or pipe, together with suitable fittings. The upper ends of the panel brace assemblies are connected to the bracing inserts after the concrete has set, and the panel is raised to a vertical position with the panel brace assemblies connected thereto. The lower ends of the panel brace assemblies then are connected to similar bracing inserts which previously were embedded in the adjacent floor slab, to thereby brace the wall panel. Additional panels are erected with their side edges adjacent to each other and are braced, in the same manner, for forming a wall. After bracing, the pickup units are disconnected from the panels. The bracing apparatus then serves to hold the panels plumb and resist wind loads while the walls are completed and a covering structure is constructed. Thereafter, the bracing apparatus is disconnected from the wall panels.
When certain wall panel dimensions and the corresponding dimensions of the panel brace assemblies are exceeded, additional bracing, termed "knee bracing", is required for bracing the panel brace assemblies. The knee bracing prevents sagging or bending of the panel brace assemblies, which would cause the panel to move out of vertical alignment and lower the resistance to wind loads. Such sagging or bending otherwise occurs due to the weight of the panel brace assemblies and wind loads. In a conventional method of bracing, a knee brace assembly or brace, similarly constructed of lumber or pipe, is connected to a panel brace assembly at a central location, and the knee brace assembly is extended downwardly therefrom and in the same vertical plane, to the wall panel. The lower end of the knee brace assembly is connected to the wall panel. In addition, lateral bracing of lumber or pipe, generally parallel to the wall panel, is extended horizontally between successive panel brace assemblies and is connected thereto at points adjacent to the knee brace assembly connections, to provide lateral brace stability.
The use of lateral bracing results in delays in construction and additional labor requirements. Thus, for example, it may be necessary to position mobile equipment such as a fork lift truck near the face of the wall panel, in order to erect components of a roof system. It then is necessary to remove the lateral bracing, to permit access of the truck, and the lateral bracing must be replaced when the truck has completed its work. Also, depending upon the design of the building, it may be necessary to erect a form for a concrete column that is cast in place after the wall panels are erected. An example is the construction of a pilaster between spaced apart side edges of adjacent panels. The column forms generally are made on the ground for the full height of the column, and then are simply lifted or pushed into position. In such cases, the lateral bracing again must be removed to allow positioning of the concrete formwork, and then replaced.